He said: "Kent Police need to urgently release this man and drop an utterly ridiculous investigation into something that has harmed no-one.

"It is not illegal to offend people and, however idiotic or insensitive the picture may have been, it is certainly not worthy of arrest.

"This case highlights the urgent need to reform a law that poses a serious risk to freedom of speech after several ludicrous prosecutions in recent months."

The arrest is the latest in a series of arrests centring on the desecration of the Remembrance Day symbol and insulting British servicemen.

In March 2011, Emdadur Choudhury, a member of Islamist group Muslims Against Crusades, was convicted after burning poppies in public in London, and exactly a year later, another man Azhar Ahmed was arrested for a Facebook post suggesting that British soldiers would go to hell.

The Crown Prosecution Service is drafting interim guidelines for prosecution of offences on social media.